A typical commercial ambient cure epoxy coating contains condensates of dimer acids with polyethylene polyamines containing more than 4 amine hydrogen atoms as a curing agent and a solution of a solid epoxy resin. This epoxy coating system has excellent flexibility, adhesion to many substrates, and resistance to water and many types of solvents. However, a problem with this system is that a solvent content of almost 50% is necessary in order to obtain a "sprayable" (Gardner D or lower) viscosity. A large fraction of such solvent evaporates from a coating, or other exposed layer of epoxy resins during cure, and thereby behaves as a volatile organic compound (VOC). Environmentally it is desirable to have low VOC content. However, it is difficult to provide a stable zero VOC aqueous dispersion of polyamine based curing agents having good cured product properties.
Solvent requirements can be reduced considerably by using a system based on liquid epoxy resin with the above polyethylene polyamine curing agent. However, even this approach still requires a system solvent level of about 30% in order to obtain a Gardner "D",or sprayable, viscosity. One way to obtain very low, or in some cases even zero, VOC content is to use a waterborne system. Standard curing agents for waterborne systems, however, are water-soluble or nearly water-soluble adducts of polyamines with epoxy resins, or else Mannich base-type amine curing agents. These materials tend to yield cured films with considerably lower flexibility and impact resistance than those provided by standard solvent-borne epoxy systems cured with polyamide-amine curing agents.
It is therefore an object of the present invention to provide a stable aqueous dispersion of a polyamide-amine curing agent which is useful for waterborne epoxy resin systems.